Derivatives and Hedging Activities - Pre-tax Gains and Losses on Derivative Contracts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Derivative [Line Items]
Amount of loss recognized in other comprehensive income (effective portion)			$ 1.1
Designated as Hedging Instrument
Derivative [Line Items]
Amount of loss recognized in other comprehensive income (effective portion)	$ 0.0	$ 0.0	1.1
Reclassification adjustment for derivative net (gains) losses included in income	0.0	0.0	1.1
Not Designated as Hedging Instrument
Derivative [Line Items]
Amount of gain recognized in other non-interest income	0.0	0.3
Amount of net fee income recognized in other non-interest income	2.5	1.3
Gain (Loss) on Fair Value Hedges Recognized in Earnings	$ 0.3	$ (0.5)
Not Designated as Hedging Instrument | Interest Rate Swap
Derivative [Line Items]
Amount of gain recognized in other non-interest income			0.0
Amount of net fee income recognized in other non-interest income			0.8
Amount of net gains (losses) recognized in mortgage banking revenues			$ (1.7)